Electrolytic color development



Jan. 31, 1967 F. VIRO 3,301,772

ELECTROLYTIC COLOR DEVELOPMENT Filed April 21,1965 3 Sheets-Sheet 1 L/ Bo A O b o b 0 A MONOLAYER, MONOCOLOR COLORFORMER DISPERSED m EMULSIONFIG] ' RECEIVING SHEET wm-l MULTICOLOR MULTILAYER WITH COLORFORMER INOIL DISPERSED IN EMULSION INVENTOR.

FELIX VIRO ATTORNEYS ,2 AGEN T Jan. 3l, 1967 Filed April 21, 1965 FIGAIF. VIRO 3,301,772

ELECTROLYTIC COLOR DEVELOPMENT I 3 Sheets-Sheet 2 BLUE RED CLEAR PATTERNOPAQUE AREA l2a If o 0 0 YELLOW l7 YELLOW FILTER 0 0 o MAGENTA llb ANIIC COLOR DEVELOPED IN A LOW pH PRIMARY AROMATIC AMINO DEVELOPER FOR ITO 5 MINUTES I 22 v COUPLER TRANSFER TO THE IMAGE RECEIVING LAYER OFRECEIVING SHEET OF FIGURE 2 BY CONTACTING EX OSED AND FIRST DEVELOPEDMULTILA ER FOR ITO 2 MINUTES AT HIGH pH WIJH A PRIMARY AROMATIC AMINODEVELOPER BLUE GREEN RED OPAQUE CLEAR IN VEN TOR.

FELIX VIRO til ATTORNEYS AGENT United States Patent 3,301,772ELECTROLYTIC COLOR DEVELOPMENT Felix Viro, Apalachin, N.Y., assignor toGeneral Aniline & Film Corporation, New York, N .Y., a corporation ofDelaware Filed Apr. 21, 1965, Ser. No. 454,240 8 Claims. (Cl. 204-2)This application is a continuation-in-part of my application, Serial No.92,017, filed February 27, 1961, now abandoned.

This invention relates to color photography and the production ofcolored photographic images. More particularly, the invention relates tocertain improvements in the development of color reproductions,especially positive color prints, of the type formed by the imagewisetransfer of colorants from an exposed original photographic element to areceiving layer.

The formation of positive colored photographic images can be effected innumerous ways and the prior art has been cognizant of these techniquesfor a long time. A method much practiced today is based on the silverhalide system of photography, wherein the production of a black andwhite image is utilized in such a manner as to regulate or control aconcomitant colored image. The source of the colored image may be acolor forming component, commonly incorporated in the photographicelement. Such a color process is referred to as color development anddepends on the reaction of the oxidation product of a primary aromaticamino developing agent with a color coupler to yield a subtractivelycolored dye image in situ with a black and white image. After removal ofthe negative silver image, the resulting negative dye image is utilizedas a pattern to form a second positive color image which corresponds tothe original color aspects of the subject being photographed. In theabove described system, it is, of course, necessary to carry out twoexposures in order to obtain a positive colored reproduction.

A more direct method for achieving a positive color reproduction makesuse of a reversal development technique. In this system of forming :apositive colored image, a multilayer color photographic film is exposedand developed with a black and white silver halide developer, such ashydroquinone. The so-obtained negative silver image is then dissolved orotherwise removed in the usual manner, thereby leaving a silver halideimage. This is next subjected to a high intensity n'on-imagewiseexposure followed by development using a primary aromatic amino typedeveloping agent, whereby color development takes place, the density ofwhich is proportional to the residual silver halide and inverselyproportional to the original exposure. After removal of the secondsilver image, there remains on the original photographic element acolored positive reproduction corresponding to the color aspects of theinitial or first exposure.

In the above described method for attaining colored positivephotographic reproductions, lengthy processing operations involvingchemical solutions are required. In the former method, two separateexposures and developments are required before the final print bearingthe colored reproduction is obtained. In the latter, i.e., the reversaldevelopment method, while not requiring the production of aninternegative, does, however, necessitate two separate developmentswhich are undesirably time consuming and uneconomical. Furthermore,unless prints are produced therefrom as an extra step, the imagesobtained by reversal development must be on a transparent for viewingthrough the base since, otherwise, the image would be reversed.

In the past few years, there has been a sharp increase in the demand forcolor prints which are of reasonably 3,301,772 Patented Jan. 31, 1967good qualit but at the same time, modestly priced. As a consequence,considerable effort is being devoted to formulating inexpensivetechniques for achieving positive colored photographic reproductions,particularly colored prints. One method which has been investigated forproducing colored photographic prints utilizes a diffusing technique incombination with a transfer material for receiving the diffused image.According to this method, a colored positive image is formed bytransferring residual or unused color developer and color coupler froman orig inal sensitive layer to a suitable receiving sheet after whichcoupling between the coupler and color former is caused to take place.The receiving layer is provided with an oxidizing agent, the purpose ofwhich is to catalyze or bring about the color forming reaction. If thissame process is utilized for producing multicolor positive images, aplurality of receiving sheets must be used, since a color separation dyeimage is formed in each receiving sheet, with the result that suchsheets must be superimposed in order to produce the final coloredreproduction. Although of academic interest, such a system is toocomplex for the commercial market, primarily because of the plurality ofreceiving sheets which make for a rather unwieldy and uneconomicaloperation. A later and improved color ditfusion process dispenses withthe plurality of receiving sheets and substitutes a single lightsensitive photographic element capable of recording all of the coloraspects of the subject. The basis of the improved diffusion system isthe utilization of color forming components, which are non-difi'usibleduring coating and negative development, but are rendered diff-usibleunder conditions of positive development. The colorless migratingcoupler image is then converted into a visible dye image at thereceiving sheet. For this purpose, the receiving sheet is convenientlyprovided with an oxidizing agent which oxidizes the paraphenylenediaminedeveloper to the active coupling form for producing the aforedescribedpositive dye image.

One of the primary disadvantages inherent in the color diffusionprocesses as above described is the high degree of discoloration due tothe stain produced when excess color developer is decomposed by theoxidizing agent. As a consequence, the so-obtained color prints are poorin quality because of high background stain caused by oxidation ofexcess developer in these areas.

I have now discovered that colored positive photographic images can beproduced utilizing the color dif fusion process without the need for anoxidizing agent which, as above pointed out, has the deleteriousproperty of causing stain and discoloration in the final color printsand the provision of such an improved color diffusion process andcompositions therefore constitute the principal object of thisinvention.

Another important object of the invention is a provision of a colordiffusion transfer process utilizing color former components, thedilfusibility of which can be controlled by adjustments in pH.

Other objects and purposes will become manifest as the descriptionproceeds.

In its broadest aspects, my invention is based on the finding that adiffusible colorant positive image remaining after negative developmentcan be transformed by electrolytic oxidation into a visible coloredpositive image, thereby reproducing the primary colored aspects of theoriginal subject. This new electrolytic process can be substituted or isapplicable to any process which utilizes chemical oxidation in order totransform a diifusible positive image into a colored visible image. Itcan be used in the color transfer process in which a color former imagediffuses imagewise to a transfer sheet whereby a visible positive imageis produced by color coupling of the diffused coupler image withoxidized color developer.

Alternately, the diffusing positive image can be a leuco dye which onmigrating to the transfer receiving material is transformed into apositive image by oxidation. In some cases, it is desirable to effectimagewise migration of a developer or a developing agent to a transferlayer having coupling components incorporated therein, whereby a coloredimage is produced by color development. My process is admirably suitedfor this latter system since the electric current is capable of bringingabout coupling between the couplers and the transfer layer and thediffusing image of the developing agent. In all of these processes,wherein the diffusing positive image is chemically oxidized to produce avisible positive image, the chemical oxidizer can be replaced orsubstituted by the electrolytic oxidation method as herein described.The process requires a relatively low potential or voltage and is,therefore, adaptable for operating within a camera since the voltage canbe provided by small dry cells of the type used in small flashlights.

The process as described herein can be operated with either directcurrent or alternating current at a potential of only a few volts. Iprefer to employ direct current since the migrating positive image isaccelerated to some extent when located in the direct current field,since it accelerates or hastens transfer of the diffusing image to thereceiving material. The electrodes which are placed in direct contactwith a layer which is to receive the diffusing image rnust be made of anelement, the oxidation potentials of which are below the potential ofthe developer or leuco dye. For this purpose, I have found copper,platinum, carbon and similar materials to be suitable. In case it isdesired to use direct current the anode or positive terminal is placedin contact with the receiving layer. Since the oxidation of colordeveloper is an irreversible reaction, it is possible to employ a lowvoltage A.C. current to bring about oxidation of the color developer.

In practicing the invention, I prefer to utilize a color diffusiontransfer system of the type described in U.S. application Serial No.816,521, filed May 28, 1959, in the name of Andre K. Schwerin and DeweyM. Dumers. According to this application, a negative colored image isfirst formed by color forming development. The residual positive imagecomposed of uncoupled color former is then caused to diffuse at elevatedpH to a receiving sheet wherein the presence of a color developer themigrating positive color former image is converted to a positive coloreddye image. The receiving sheet contains an oxidizing agent whichoxidizes the color developer and thus provides the oxidized or reactivespecies of the developer which couples with the color former image. Inthe color diffusion transfer process as described herein, I employ, inlieu of the chemical oxidizers of the application, a low voltageelectric potential applied to the receiving layer. The color developingagent is quickly and easily oxidized to the reactive form which thenreacts with the diffused color former image with concomitant productionof a positive colored photographic reproduction.

The color formers which are used in practicing the color diffusionprocess as described in the aforementioned application are especiallydesigned for this system, it being particularly important that thecouplers diffuse at higher pH, i.e., 12.5-13.0, but remain relativelyimmobile at lower pH values. Specifically, the color formers which areused in this diffusion process must possess the following attributes:

(1) Medium molecular weight (2) Freedom from water-solubilizing groupssuch as carboxy or sulfonic acid functions (3) Sufficient oil solubilityto \be incorporated in resinous or oily packets (4) Contain such groupsas phenolic or enolic hydroxy which form coupler salt at a high pH(12.5-13.0) which metal salt renders the color former moleculesdiffusible in aqueous medium (5) Produce non-diffusible dyes withconventional primary aromatic amino developing agents such asN-diethylp-phenylenediamine;N-ethyl-N-fi-hydroxy-ethyl-p-phenylenediamine andN-diethyl-3-methyl-p-phenylenediarnine, and the like Examples ofcouplers which can be utilized in connection with the above describedcolor diffusion process can be formulistically depicted as follows:

(1 olrn o o H I o- NHC 0 H30 \N/ (II/- I occurs after the positive imageis formed, the production of stain and discoloration is minimized. Theinstant technique, therefore, represents -a decided advance over theprior art in presenting a simplified method of producing positivecolored photographic images without the need for several stages orprocessing. As has previously been pointed out, such conditions areespecially important if colored prints are to be produced by developmentwithin the camera itself.

The invention will be more fully understood by reference to theaccompanying drawings in which:

FIGURE 1 discloses in section an elevational view of a mono-layercontaining on a clear film or paper support a coating of a gelatinosilver halide emulsion having uniformly dispersed therein oily packetscontaining dissolved color former according to the invention;

FIGURE 2 shows in section an elevational view of a transfer sheetconsisting of a conducting support having coated on one of its surfacesa receiving layer of gelatin or a similar photographic colloid carrier;

FIGURE 3 depicts in section an elevational view of a multilayer coatingin which each of the layers contain a differently sensitized silverhalide emulsion having uniformly dispersed therein oily packets ofdissolved color former;

FIGURE 4 is a flow sheet illustrating the steps of: (A) Exposing,

(B) Color developing to a negative image the multilayer coating ofFIGURE 3,

(C) Transferring the unreacted color former from the first developmentto the transfer sheet,

(D) Forming the colored positive photographic image produced by thecoupling of the diffused color formers with electrolytically oxidizedcolor developer,

FIGURES 5, 6 and 7 are schematic views, partly in cross-section,depicting various forms of electrodes in contact with the receivingsheet undergoing development.

' FIGURES 1 and 3 of the drawings are believed to be self-explanatorywhen his understood that reference character ltl'represents the base ofthe sensitized elements of FIGURES land 3. Reference character 11represents the light-sensitive emulsion layers having distributedthrough the colloid carrier 14 oily packets of dissolved color former 12and silver halide grains 13. FIGURE 2 depicts the receiving sheet 25comprising the base 10a which carries thereon the receiving layer 15.

In FIGURE 4,,the multilayer coating depicted in FIG- 3 is exposed to apattern representing the primary colored aspects'of a subject. Referringto the flow sheet, for FIGURE 4, A depicts the exposure step and the recording of the latent primary images in the three sensitized layers. 16represents a blue latent image, 17 the green and 18 the red. The opaquearea of the pattern forms no images in the sensitized layer; under theclear area of the pattern, latent images are formed in each layer.

In accordance with the invention, the exposed photographic element of Ais developed in a low pH primary aromatic amino developer for 1-5minutes, whereby a negative colored image and a negative silver image isrecorded at 20, the green image 21 and the red at 22. These are thesubtractively dyed images of negative development and as dye images arenon-diffusing under pH conditions of the first development. The exposedand first developed layer is then developed in a second developercontaining a primary aromatic amino developing' agent under elevated pHconditions, whereby the couplers not utilized for dye formation in firstdevelopment are rendered diffusible in the higher alkaline medium of thesecond development. After allowing second development to proceed for 1-2minutes, the receiving sheet of FIGURE 2 is placed in contact with theupper layer of the exposed 3-layer coating whereby the migrating couplerimage is imbibed on the image receiving layer of the receiving sheet.The receiving sheet, which now contains the diffused color former imagein addition to imbibed c-olor developer, is placed between theelectrodes of a low voltage potential wherein the anode is connected tothe image receiving sheet and the cathode is connected to the support ofthe receiving sheet. Under the action of the low voltage current, theprimary aro matic amino developing agent is oxidized to the reactivecoupling form which reacts with the diffused color forming image to formon the receiving layer of visible positive colored reproduction of theoriginal subject matter being photographed.

In carrying out the electrolytic development of the receiving sheet, theelectrodes may consist of a pair of rollers 26 and 27 as shown in FIGURE5, having electroconductive surfaces which are pressed against theopposite sides of the receiving sheet 25. The latter passes between therollers as the latter rotate, the conductive surface of roller 26 beingconnected to the anode and that of roller 27 to the cathode of a source28 of low DC. voltage. The sheet 25 has its base 10A in contact with thecathode roller 27, and its receiving layer 15 in contact with the anoderoller 26.

Alternatively, as shown in FIGURE 6, the cathode roller 27 may bereplaced by a cathode-connected plate 29 on which the receiving sheet 25is supported with its base 10A in contact with plate 29. Ananode-connected roller 30, similar to roller 26, is passed over thereceiving surface 15 of the receiving sheet 25 to effect developmentthereof.

Instead, if desired, both rollers can be replaced by electricallyconductive plates 31 and 32, connected respectively to anode and cathodeof a low voltage D-.C. source, and pressed respectively against thereceiving side 15 and the base 10A of the receiving sheet 25.

The rollers of FIGURES 5 and 6 are of such length, and the plates ofFIGURES 6 and 7' of such dimensions, as to contact (progressively in thecase of the rollers, and simultaneously in the case of the plates) theentire image-bearing area of the receiving sheet 25 when the latter ispassed between or under the rollers or lies in contact with the plates.

The following examples will further explain the invention, although itis to be understood that the invention is not restricted to suchexamples.

Example I One coating was prepared in which the average size of the oilypacket Was less than 1 micron. This coating was prepared by dissolvingten millimoles of a cyan color former of the following formula:

In 30 g. of tricresylphosphate and dispersing this solution in 120 ml.of a 6% aqueous gelatin solution to which had been added 0.5 ml. oflauryl sulfate (25% solution). Homogenation of the oily coupler solutionwas affected by agitation in a Waring Blendor. The dispersion obtainedin this manner was then mixed by the gentle stirring with 300 g. of agelatino silver chlorobromide emulsion containing 6% silver halide andthe mixture coated on a clear filmbase such as cellulose triacetate. Theusual coating finals known to the art can be incorporated at this point.

& After drying the coating was exposed in a step-wedge sensitometer anddeveloped to maximum density for 5 minutes at 20 C. in the followingdeveloper:

Sodium hexametaphosphate 'g 1 Sodium sul-fite g 8N-ethyl-N-fi-hydroxyethy1-p phenylene diann'ne -g 5 Sodium carbonate,monohydrate ..g 10 Sodium bromide g 1 Water to make cc 1000 Thisdeveloper has a pH of 10.7.

The developed strip without washing is pressed into contact for 3minutes with a transfer sheet of b aryta coated paper which had beenpreviously presoaked for 5 minutes in a 2% solution of sodium hydroxide.Contact between the developed strip and transfer sheet is convenientlyeffected by means of power driven pressure rollers as is well known inthe art. The purpose of presoaking the transfer sheet with alkali is toprovide the necessary high pH :to effect diffusion of the coupler image.After aprpoximately 1 minute contact with the receiving layer, transferof the coupler to the receiving sheet has reached equilibrium and theimage receiving sheet is separated and brought in contact with {theelectrodes connected to a low voltage D.C. source in such a manner thatthe anode is in immediate contact with the gel layer of the imagereceiving sheet. As electrodes there may be used any of the arrangementsshown in FIGURES 5, 6 and 7. Under the action of the low voltagecurrent, electrolytic oxidation of the developer takes place withimmediate coupling mm the diffused color former image resulting in theproduction of a positive cyan colored image.

Example II Utilizing the procedure as given in Example I, a positivemagenta image was produced by substituting a magenta color former of thefollowing (formula:

The procedure and results paralleled those of Example I with theexception that the positive colored image was magenta.

Example III A yellow image was produced by following the procedure ofExample I except the cyan color former of the first example was replacedby yellow color former of the following structure:

The results and procedure paralleled those of the first example with theexception that the positive color image was yellow.

Example IV This example i lustrates the utilization of a three-layercoating as illustrated in FIGURE 3 which is composed of threediiferently sensitized silver halide coatings on a base each coatingsensitized one of the primary color regions of the visible spectrum. Inpreparing a multilayer color reproduction photographic element, a barytatreated paper base is coated with the composition described in Example Iin which the silver bromo chloride emulsion containing 6% silver halide,is sensitized with a red sensitizer of the following structure:

S H300 I I OCHs t H t i l moo -o=oo 1 00113 On top of the red sensitivelayer is applied a green sensitive layer which is the compositiondescribed in Example II wherein the silver halide is sensitized with asensitizer for the green of the type described in US. Patent 2,295,-276. On top of the green sensitive layer is applied a 3% gela-tinoseparation layer containing yellow colloidal silver as a yellow filter.The upper blue sensitive layer is formed by coating over the filterlayer the silver halide yellow color former dispersion described inExample III. The resulting multilayer coating is illustrated in FIGURE 4of the drawing. The dried coating is exposed to an image or a stepwedgesensitometer and processed in the following manner:

The exposed negative image was developed for 5 minutes at 25 C. in thesolution of the following composition:

2-amino-S-diethylaminotoluene g 4.0 Sodium sulfite g Borax g 5 Sodiumhydroxide g 1.5 Benzyl alcohol cc 3.0 Sodium bromide g 0.5 Water 1000cc.

The developed image was then brought in contact with the receiving sheetin the following high pH developer:

2-amino-S-diethylaminotoluene g 4.0 Sodium sulfite g 20 Sodium hydroxideg Sodium iodide g 80 Water 1000 cc.

After three minute contact the receiver was separated and the positiveimage was developed electrolytically as described in Example I.

Example V Light-sensitive materials are prepared as in Examples I-IV,with the only exception of keeping silver halide and color former ratioin the emulsion to 8:1. In this case, the light-sensitive material,after receiving an imagewise exposure, was developed for 90 seconds inthe following high pH developer, after which it was brought in contactwith image receiving sheet and then was processed as described inExamples I-IV:

2-amino-5-diethylaminotoluene g 4.0 Sodium sulfite g Sodium hydroxide g15 Sodium bromide g 2.5

Water 1000 cc.

A full colored reproduction of the original subject is reproduced on thereceiving layer. It will be evident that the process contemplated hereincan be brought about in a camera or similar copying device. The onlyrequirements are the ability to expose the sensitized material, developthe same, and to contact the developed material at a high pH with atransfer sheet.

If it is desired to increase the rate of diffusion of the colorant imagewhile effecting simultaneous development thereof, it is necessary tohave in contact with the image receiving layer a material, the oxidationpotential thereof being less than that of the oxidizable colorant.Specifically, a layer, having an oxidation potential as above described,can be interpolated between the image receiving layer and the support.Alternately, the support itself may be made of a material having therequired oxidation potential Whereas most of the examples as describedherein specify gelatin as the colloid carrier, it will be understoodthat other gelatin substitutes can be used and, in this connection,mention is made of polyvinyl alcohol, methyl cellulose, casein, andother gelatin substitutes well known to those skilled in the art. a

It may be added that the color formers which are employed are thosewhich are capable of forming nondiffusing quinonimine or azomethine dyeimages upon color development with a primary aromatic amino developer.These color formers are pyrazolones, phenolic derivatives, or straightchain keto methylene compounds. They must not only possess suchstructural features but must also meet the attributes previouslyspecified. By using a leuco dye, which is non-diffusing in the oxidizedform, but diffusing in the leuco form at high pH,a color positive imagecould be obtained by a process similar to Example 1.. However, thedeveloper solution would not include the color developer since thediffusing leuco image itself would be the source of a final coloredpositive image.

My electrolytic development process could be utilized to produce animage in light sensitive layers by the use of conventional color formersor leuco dyes if the light sensitive layers are capable of causingimagewise change in conductivity of the colloid layer, upon exposure tolight, heat or other source of radiant energy.

Modifications of the invention will occur to persons skilled in the artand I, therefore, do not intend to be limited in the patent grantedexcept as necessitated by the appended claims.

. I claim:

1. A process of forming a positive multicolor photographic reproductionwhich comprises exposing to the color aspects of a subject aphotographic material comprising a suitable support carrying at leastone light sensitive photographic silver halide emulsion layer,containing a coupler compound capable of forming a dye when reacted withthe oxidation products of a primary aromatic amino silver halidedeveloping agent, and said coupler compound being characterized byrelatively high diffusibility at elevated pH, developing the exposedemulsion layers in the presence of said developing agent at a pH below12.5, to form non-dilfusible dye images in those areas corresponding tolight-exposure, transferring the diffusible invisible positive image ofcolor coupler by imbibition at an elevated pH above 12.5 to a receivinglayer having therein a primary aromatic amino silver halide developingagent, applying a relatively low voltage electrical potential to thetotal moist surface of said receiving layer, the potential of which issufiicient to bring about electrolytic oxidation of the developing agentto form oxidized developing agent which reacts with the positive imageof diffusing color former to produce a positive dye image correspondingto the color aspects of the subject.

2. A process of forming a positive multicolor photographic reproductionwhich comprises exposing to the color aspects of a subject, aphotographic material comprising a suitable support carrying at leasttwo superhuposed silver halide emulsion layers sensitized to differentregions of the electromagnetic visible spectrum, each layer beingfurther provided with a different coupler compound capable of forming adye when reacted with the oxidation products of a primary aromatic aminosilver halide developing agent, and said coupler compound beingcharacterized by relatively high dilf-usibility at elevated pH,developing the exposed emulsion layers in the presence of saiddeveloping agent at a pH below 12.5, to form non-difliusible dye imagesin those areas corresponding to light exposure, transferring the diflusible invisible positive images of the color couplers by imbibition atan elevated pH above 12.5 to a receiving layer having therein a primaryaromatic amino silver halide developing agent, applying a relatively lowvoltage electrical potential to the moist imbibed surface of saidreceiving layer, the potential of which is sulficient to bring aboutelectrolytic oxidation of the developing agent to form oxidizeddeveloping agent which reacts with the positive image of the diffusingcolor formers to produce a positive dye image corresponding to the coloraspects of the subject.

3. A process of torming a positive multicolor photographic reproductionwhich comprises exposing imagewise to a col-or object a photographicmaterial comprising a suitable support, three superimposed silver halideemulsion layers sensitized to dilferent regions of the visible spectrum,each layer containing a color ttormer capable of forming when reactedwith the oxidation products of a primary aromatic amino silver halidedeveloping agent, a dye image complementary in color to that color towhich silver halide emulsion layer is sensitized, and wherein the lowestemulsion layer is sensitized to red light and contains a color formercapable of forming a cyan image, a middle layer sensitized to greenlight and containing a color former capable of forming a magneta image,and a top layer sensitive to blue light and containing a color formercapable of forming a yellow image, said color tiormers beingcharacterized by a relatively high diffusibility at a pH above 12.5;developing the exposed emulsion layers in the presence of saiddeveloping agent or a pH ibelow 12.5 to form non-diffusible dye imagesin those areas exposed by light, transferring by imbibition in a mediumhaving a pH above 12.5 the ditEusi-ble residual color formers in theunexposed areas to the total wet surface a receiving layer havingtherein a primary aromatic amino silver halide developing agent;applying uniformly a relatively low voltage electrical potential to theimbided moist surface of said receiving layer, the potential of which issufficient to bring about electrolytic oxidation of the developing agentto 'form the 12 oxidized developing agent which reacts with thedifi'used color formers to produce a positive multicolor dye imagecorresponding to the color aspects of the subject in the receivinglayer.

4. The prcess according to claim 2 wherein the photographic elementcomprises three superimposed silver halide photographic layers eachsensitized to one of the primary colors of the electromagnetic visiblespectrum, and each emulsion layer having a color coupler compoundcapable of forming substractively color dye images on first development.

5. A process as defined Iby claim 3, wherein a yellow filter layer isinterposed between the green sensitive layer and the blue .sensitivelayer.

6. A process as defined in claim 2, wherein the low voltage electricalpotential is provided by a direct current source.

7. A process as defined in claim 6, wherein the anode of that directcurrent source is applied to that side of the image receiving sheetwhich faces the multilayer material and to which the diffused colorformers are transferred.

8. A process as defined by claim 2, wherein the low voltage electricalpotential is provided by an alternating current source.

References Cited by the Examiner UNITED STATES PATENTS 2,43 0,254 ll/1947 Solomon 204Z 2,756,142 7/ 1956 Yutzy 96--3 3,220,836 11/ 1965Fair-bank 96-29 FOREIGN PATENTS 3 ,47 8 11/ 1960 Great Britain.

NORMAN G. TORCHIN, Primary Examiner.

J. TRAVIS BROWN, Examiner.

1. A PROCESS OF FORMING A POSITIVE MULTICOLOR PHOTOGAPHIC REPRODUCTION WHICH COMPRISES EXPOSING TO THE COLOR ASPECTS OF A SUBJECT A PHOTOGRAPHIC MATERIAL COMPRISING A SUITABLE SUPPORT CARRYING AT LEAST ONE LIGHT SENSITIVE PHOTOGRAPHIC SILVER HALIDE EMULSION LAYER, CONTAINING A COUPLER COMPOUND CAPABLE OF FORMING A DYE WHEN REACTED WITH THE OXIDATION PRODUCTS OF A PRIMARY AROMATIC AMINO SILVER HALIDE DEVELOPING AGENT, AND SAID COUPLER COUMPOUND BEING CHARACTERIZED BY ELATIVELY HIGH DIFFUSIBILITY AT ELEVATED PH, DEVELOPING THE EXPOSED EMULSION LAYERS IN THE PRESENCE OF SAID DEVELOPING AGENT AT A PH BELOW 12.5, TO FORM NON-DIFFUSIBLE DYE IMAGES IN THOSE AREAS CORRESPONDING TO LIGHT-EXPOSURE, TRANSFERRING THE DIFFUSIBLE INVISIBLE POSITIVE IMAGE OF COLOR COUPLER BY IMBIBITION AT AN ELEVATED PH ABOVE 12.5 TO A RECEIVING LAYER HAVING THERIN A PRIMARY AROMATIC AMINO SILVER HALIDE DEVELOPING AGENT, APPLYING A RELATIVELY LOW VOLTAGE ELELCTRICAL POTENTIAL TO THE TOTAL MOIST SURFACE OF SAID RECEIVING LAYER, THE POTENTIAL OF WHICH IS SUFFICIENT TO BRING ABOUT ELECTROLYTIC OXIDATION OF THE DEVELOPING AGENT TO FORM OXIDIZED DEVELOPING AGENT WHICH REACTS WITH THE POSITIVE IMAGE OF DIFFUSING COLOR FORMER TO PRODUCE A POSITIVE DYE IMAGE CORRESPONDING TO THE COLOR SPECTS OF THE SUBJECT. 